The present invention relates to a device for the selective acquisition of signals which succeed one another in time and which can be located by the addresses associated with their relative positions, with a view to their characterization by a digital computer. It also relates to a television signal acquisition apparatus using the said device. The invention is more specifically applicable to the characterization of television signals.
The characterization of a signal and particularly a television signal is conventionally carried out by standard measuring devices, such as osciloscopes, or more specialized devices, such as vectorscopes, noise meters, video voltmeters, etc. Most of these devices can be replaced by a signal acquisition device coupled to a digital computer and to a graphic display means, which in the present state of the art represents a significant reduction in costs and an improvement in performance levels.
However, when the acquired signal lasts for a relatively short time of approximately 100 microseconds, digital computers cannot give direct access to the signal, transmitted to them by the acquisition device. These problems, which are mainly encountered in television, are mainly due to the analog format of the signal, whose duration is 64 microseconds in the 625 line system, to the extensive spectrum thereof and to the limited processing speed of existing digital computers, which are limited in their performances both with respect to the acquisition levels, the orienting of the data in the memory and the processing times, and with regards to the read-out of the results by the instruction performance times, which would appear to be long, i.e. 10 microseconds, compared with the duration of the signal.
However, high speed analog-digital conversion means are known enabling a computer to acquire a portion of a television signal. Such means generally comprise a converter able to work on samples composed of a reduced number of bits, generally 8 bits, at high frequencies of approximately 25 MHz and a buffer store able to store one or two television lines. The acquisition of the signal takes place in real time on one or both lines and a transfer of the stored samples into the buffer store takes place to the computer at a much lower speed. Such means do not permit a very faithful acquisition of the signal, particularly measuring and test signals, which are necessary for a precise characterization of the signal.